Fiorentina eased to a 3-0 win over 10-man Atalanta to move into sole possession of top spot in Serie A after Inter Milan drew 1-1 at Sampdoria earlier Sunday.
Atalanta was down to 10 men in the fifth minute when Gabriel Paletta was sent off and Josip Ilicic fired Fiorentina in front from the penalty spot. Borja Valero and Joan Verdu secured the points.
After its best ever start to a Serie A season, Fiorentina was two points ahead of Inter and three ahead of Lazio, which beat Frosinone 2-0. Roma was a point further back after winning 4-2 at Palermo following a double from Gervinho.
"I like being honest," Fiorentina coach Paulo Sousa said when asked about his side's title chances. "I believe there are better teams than us but we'll try to compete with them too."
Sami Khedira marked his Serie A debut with a goal to help four-time defending champion Juventus to only its second league win of the season as it came from behind to beat bottom side Bologna 3-1, but there was more misery for AC Milanwhich was thrashed 4-0 at home by Napoli.
It was Khedira's second match in a week after helping Juventus to a 2-0 victory over Sevilla in the Champions League on Wednesday. The German World Cup winner, who had been out of action for two months with a thigh injury, brings much-needed experience to the team.
"It was an important win, I'm happy for my goal but above all for the three points," Khedira said. "It's not only down to me that we've won two matches with me on the pitch, but down to the whole team. Juventus needs 11 leaders, not just one."
Elsewhere, Sassuolo saw its unbeaten run end with a 1-0 loss at Empoli and Udinese drew 1-1 against Genoa. Udinese striker Antonio Di Natale, who had his head heavily bandaged following an earlier collision, scored his 208th Serie A goal.
Atalanta hadn't won in Florence since 1993 and any hopes they had of overturning that record disappeared when Paletta was sent off after he and teammate Alejandro Gomez tangled with Jakub Blaszczykowski, and Ilicic sent goalkeeper Marco Sportiello the wrong way.
Borja Valero hit the crossbar before doubling Fiorentina's lead in the 34th following a swift one-two with Federico Bernardeschi.
Verdu capped a great night for Fiorentina with his debut goal after a delightful flicked assist from Nikola Kalinic - last week's hat-trick scorer against Inter.
Napoli's biggest ever victory over Milan was watched by the NBA's Boston Celtics, who are in town for Tuesday's match against Olimpia Milano.
Lorenzo Insigne scored two goals and set up Allan's opener before Rodrigo Ely's own goal completed a bad night for Milan.
Juventus was looking to turn its league campaign around after five points from six rounds, despite a perfect record in the Champions League.
It was given an early scare when Anthony Mounier's powerful shot squirmed under Gianluigi Buffon to put Bologna ahead in the fifth minute.
Alvaro Morata leveled in the 33rd when he was left completely unmarked to head home Khedira's deflected cross.
The Spaniard was also involved in Juve's other goals. Morata won the penalty which Paulo Dybala converted - after making the most of a slight tug by Bologna defender Alex Ferrari - and put a diagonal pass into the area for Khedira to nod home.
Inter was looking to get back on track after seeing its perfect start to the season shattered last week but it was Sampdoria which had the best of the first-half chances and Joaquin Correa had the worst miss of the season so far in the 38th minute.
Correa was one-on-one with Samir Handanovic and his effort took a lucky ricochet off the Inter goalkeeper to leave the Argentine midfielder in front of an open goal but he sent his effort wide of the far post from two yards out.
Luis Muriel atoned for his teammate's error early in the second half, volleying in a cross from 17-year-old Pedro Pereira.
Inter leveled 14 minutes from time in somewhat chaotic fashion. Mauro Icardi's volley took a double ricochet but he was able to prod the rebound into the path of Ivan Perisic, who poked it into the bottom corner for his first Serie A goal.